U.S. researchers say they've used a laser to stop the tumbling motion of a molecule, a breakthrough that could lead to extremely fast quantum computers.

Shining a laser onto a trapped but moving molecule instantly cools it to temperatures found in outer space -- around minus 452 degrees Fahrenheit -- causing it to stop its rotation, scientists at Northwestern University are reporting.

Controlling molecules in this way, the ability to govern their rotational and vibrational states, is essential if they are to be used in superfast quantum computers, many times faster than the fastest computers today, they say.

Trapping molecules and holding them precisely in a set location isn't all that difficult, but the problem is that they will persist in continuing to rotate as if they had not been confined at all, the researchers note.

The Northwestern team has managed to build a custom laser that can cool charged molecules of aluminum monohydride from a starting point of room temperature down to a frigid minus 452 degrees Fahrenheit in less than a second.

Ongoing tumbling motion of the molecule is stopped in its tracks, they report in the journal Nature Communications.

"It's counterintuitive that the molecule gets colder, not hotter when we shine intense laser light on it," says research leader Brian Odom, an assistant professor of physics and astronomy. "We modify the spectrum of a broadband laser, such that nearly all the rotational energy is removed from the illuminated molecules."

Although such control of molecules has been achieved before -- usually with cumbersome setups that require massive cooling with liquid helium -- the Northwestern experiment is the first to cool a molecule down to its lowest quantum rotational level by means of a room-temperature apparatus, the researchers say.

Singly charged aluminum monohydride molecules were chosen because they do not vibrate when they interact with a laser, allowing the researchers to concentrate on stopping rotation without having to also deal with vibration.

"If I want to slow down a molecule, quantum mechanics tells me that it happens in steps," Odom says. "And there is a very lowest step that we can get the molecule down to, which is what we've done."

Inexpensive aluminum monohydride molecules could have an extensive range of uses beyond applications in quantum computing, Odom says.

"There is a lot you can do if you get one species of molecule under control, such as we've done in this study," he says. "We are the first to stop molecular tumbling in such a powerful yet simple way."

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